Horizontal Roof Drain Pipe Sizing

Take the roof s total square footage and divide by the total square footage handled by one drain.

Horizontal roof drain pipe sizing.

To convert to an area for use in table 1108 2 do this. Roof drain connected to a 6 in. Roof drain vertical requirement for horizontal roof areas at various rainfall rates leader size hourly rainfall in inches pipe open 1 1 1 2 2 2 1 2 3 4 5 6 7 8 size area inches sq. For example a 4 in.

A minimum 5 inch diameter drain on a 1 4 inch per foot slope is required. Roof drain connected to an 8 in. The minimum size of any building drain serving a water closet shall be 3 inches. A 5 inch diameter pipe with a 1 4 inch per foot slope will carry 4 720 sq ft.

Adequate drainage is an important component of a properly installed roof so installing the correct size of drains is essential. For example in the u k. Horizontal drain 5 000 sq ft. 50 000 4 400 11 36.

The roof drainage outlets and rainwater downpipes are calculated based on the design principles for gravity drainage systems established in ss525 2006 code of practice for drainage of roofs. Section 101 5 of the ipc tells us not to reduce the pipe size in the direction of flow. Designers specify compliance with bs en 12056 3 2000 that includes a calculation for the allowable capacity of the rainwater pipes. The roof drain or gutter or drain piping or downspout leader size diameter other size constraints e g.

The result is the number of drains needed. Or 12 drains required. 1 inch 25 4 mm 1 inch per foot 83 3 mm m. Enter table 1108 2 until youfind a diameter pipe that will carry 4 688 sq ft.

Or less in diameter the piping will be larger in diameter than the roof drain. Zurn plumbing products groupspecification drainage operation 1801 pittsburgh avenue erie pa 16502 phone 814 455 0921 fax. The calculations below are meant for drainage from flat roofs where water are expected to spread over the entire flat roof during rain. The maximum number of drainage fixture units connected to a given size of horizontal branch or vertical soil or waste stack shall be determined using table 710 1 2.

5 000 4 x 3 75 4 688 sq ft. Following this logic it is possible that for roof drains 6 in.